Each day workers put themselves at risk by working in dangerous or potentially dangerous environments involving explosive vapors or gasses. For example, in addition to the risk of cave-ins, sub-surface miners face the risk toxic fumes and explosive gases on a daily basis. As another example, firemen and other first responders frequently have to venture into buildings, subways and sewers filled with explosive gasses in order rescue victims and save property.
Chief among the dangers facing such workers is the possibility of an explosion due to detonation of explosive vapors, gasses and dust suspended in the air in a confined space. One of the top causes of mine explosions is the detonation of explosive gases, such as methane, which can enter the mine through the Earth that is being mined. If proper ventilation procedures are not taken, methane gas (or other explosive gases) may collect in the mine. Any ignition source may explosively ignite the gas and lead to catastrophic results.
Fire and rescue personnel face similar dangers when hurricane, tornado or terrorist attacks leave buildings in ruble with natural gas lines leaking. As another example, fire and rescue personnel responding to refinery incidents, and automobile and aircraft accidents can face explosive vapor situations resulting from gasoline and diesel fumes. While gas and vapor levels in one part of a building appear safe, gas and fumes can accumulate in pockets, pits or enclosed rooms to reach potentially explosive concentrations.
In addition to explosive gases, combustible dust can give rise to an explosive environment. Such dust explosion risks can arise in a variety of situations such as factory mishaps, grain milling and storage facilities.
In addition to fire and rescue personnel, many work environments require communications in the presence of explosive gasses and vapors. The Occupational Safety and Health Administration (OSHA) has classified a number of hazardous work environments where special precaution must be taken to provide workers with safe working conditions. The most extreme work environment is classified as Class I, Division 1. A Class I, Division I work environment is a location in which: (a) hazardous concentrations of flammable gases or vapors may exist under normal operating conditions; or (b) hazardous concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage; or (c) breakdown or faulty operation of equipment or processes might release hazardous concentrations of flammable gases or vapors, and might also cause simultaneous failure of electric equipment.
Examples of work locations where Class I, Division I classifications are typically assigned include: locations where volatile flammable liquids or liquefied flammable gases are transferred from one container to another; interiors of spray booths and areas in the vicinity of spraying and painting operations where volatile flammable solvents are used; locations containing open tanks or vats of volatile flammable liquids; drying rooms or compartments for the evaporation of flammable solvents; locations containing fat and oil extraction equipment using volatile flammable solvents; portions of cleaning and dyeing plants where flammable liquids are used; gas generator rooms and other portions of gas manufacturing plants where flammable gas may escape; inadequately ventilated pump rooms for flammable gas or for volatile flammable liquids; the interiors of refrigerators and freezers in which volatile flammable materials are stored in open, lightly stoppered, or easily ruptured containers; and all other locations where ignitable concentrations of flammable vapors or gases are likely to occur in the course of normal operations.
For personnel who work in such environments on a daily basis, a communication system is needed that can safely operate in explosive environments. Similarly, emergency services personnel who may have to enter explosive environments to respond to emergency situations need a deployable explosion-proof communication system. Cellular telephones would normally provide cost effective and reliable communications, but cellular signals may not penetrate buildings, sewers and mines where workers and emergency services personnel may need to travel. Conventional methods for boosting and relaying cellular communications cannot be used in explosive environments because they could spark an explosion. Additionally, conventional cellular telephones may serve as ignition sources and so cannot be safely taken into an explosive environment.